Method for machining a workpiece made of a metallic material

ABSTRACT

A method for machining a workpiece made of a metallic material, in which the workpiece is machined by ECAP, characterized in that after the machining by ECAP, the workpiece is post-processed by hammering, thus achieving a diameter reduction. As a result, material properties of the material of the workpiece and in particular the strength and the hardness may be significantly increased.

The invention relates to a method for machining a workpiece made of ametallic material, in which the workpiece is machined by ECAP.

Methods for machining workpieces are known which are summarized underthe name “severe plastic deformation” (SPD). This involves a method inwhich a workpiece made of metal is subjected to severe plasticdeformation in order to produce an ultrafine-grained (UFG) structure.The structure may attain an average grain size of less than 1 μm, andoften has large orientation angles at the grain boundaries. The SPDmethods include, among others, equal channel angular pressing (ECAP),accumulative roll bonding (ARB), high pressure torsion (HPT), repetitivecorrugation and straightening (RCS), cyclic extrusion compression (CEC),torsion extrusion, severe torsion straining (STS), cyclic closed-dieforging (CCDF), and super short multi-pass rolling (SSMR).

ECAP is a method in which a workpiece is pressed through at least twointermerging channels, wherein the channels have an identical crosssection, and the transition between the channels is angled at anarbitrary angle, preferably between 80° and 140°. The plasticdeformation of the material of the workpiece when pressed through thetransition between the channels may result in a marked refinement of thematerial structure, and thus, improved material properties. Machining ofa workpiece by ECAP is described in U.S. Pat. Nos. 5,513,512 A,6,399,215 B1, and EP 2 366 808 A2, for example, wherein the machinedworkpieces are made, at least partially, of (pure) titanium and/or areused for manufacturing medical implants.

Medical implants are often made of pure titanium, which has very goodbiocompatibility. However, the relatively low mechanical strength ofthis material may be disadvantageous in such implants. Although themechanical strength may be increased significantly by the use oftitanium alloys, this generally occurs at the expense ofbiocompatibility, and thus possibly of the dwell time of titanium alloyimplants in a human or animal body.

The devices used in the above-cited publications for carrying out ECAPare limited with respect to the dimensions and in particular withrespect to the length of the workpieces to be machined. This isattributed in particular to the limited stroke of the stamp with whichthe workpieces are pressed through the channels of the particular tools.For eliminating this disadvantage, according to U.S. Pat. No. 7,152,448B2 a suitable device is proposed, in which the workpiece has a first,partially circular channel that merges at an angle into a second,straight channel, wherein the first channel on the radially inner sideis delimited by a rotatingly drivable, disk-shaped propulsion element.By rotation of the propulsion element, the workpiece is moved throughthe first channel by frictional engagement and pressed into the secondchannel in a continuous process. The aim is to allow machining ofworkpieces, having any length in principle, by ECAP in a continuousprocess.

In the publication “Severe Plastic Deformation by Equal Channel AngularSwaging” in Material Science Forum, Vols. 667-669, pages 103-107 (ISSN:1662-9752) by Bruder et al., a method referred to as ECAS is describedwhich combines the principles of ECAP and hammering (rotary swaging);however, the rotation of the workpiece relative to the tools, which ischaracteristic of conventional hammering, is not carried out. Inaddition, in the ECAS method the modified hammering always takes placeconcurrently with the ECAP. Diameter reduction for the workpiece is notachieved in the ECAS method.

US 2007/0256764 A1 discloses machining of a workpiece by a methodreferred to as ECAE, comparable to ECAP, in which the workpiece or theECAE tool is set in vibration during the machining. This generation ofvibration does not result either in deformation of the workpiece, or inparticular diameter reduction. In addition, there are no forming strokesby forming tools during the generation of vibration.

In the publication by Pachla et al., “Effect of severe plasticdeformation realized by hydrostatic extrusion and rotary swaging on theproperties of CP Ti grade 2” in Journal of Material ProcessingTechnology 221 (2015), pages 255-268, a method is described whichcombines hydrostatic extrusion with post-processing of a workpiece byhammering. The hammering is carried out to improve the surface qualityof the workpiece.

Based on this prior art, the object of the invention is to provide amethod by means of which in particular mechanical material properties ofa workpiece that is machined by ECAP may be further improved.

This object is achieved by a method according to Patent claim 1.Advantageous embodiments of the method according to the invention andadvantageous uses of a workpiece produced according to the invention arethe subject matter of the further patent claims, and/or result from thefollowing description of the invention.

According to the invention, a method for machining a workpiece that ismade of a, or at least one, metallic material or contains such, whereinthe workpiece is machined by ECAP, is characterized in that after themachining by ECAP, the workpiece is post-processed by hammering, thusachieving a (permanent) diameter reduction due to plastic deformation ofthe material of the workpiece. It has surprisingly been found thatmechanical material properties of the material of a workpiece previouslymachined by ECAP, in particular its tensile strength and/or hardness,may thus be significantly improved or increased. This finding wassurprising in particular due to the fact that other methods forpost-processing forming, for example rolling, of a workpiece previouslymachined by ECAP do not always result in these improvements; on thecontrary, improvements in the mechanical material properties previouslyachieved by ECAP are diminished, depending on the degree of deformation.Even when there is an improvement, usually only the strength isincreased whereas the ductility is severely reduced, and whenoverloaded, the material becomes brittle or fractures with very littledeformation. Such materials are not suitable as construction materials.

As stated above, machining by ECAP has basically been characterized inthat a workpiece is pressed through at least two, or even three or more,intermerging channels, wherein the channels preferably have an identicalcross section and the transition between the channels is angled. Theplastic deformation of the material of the workpiece when passingthrough the transition between the channels may result in significantrefinement of the material structure, and thus, improved materialproperties. In particular, the tensile strength and/or the hardness ofthe material may thus be greatly increased compared to the startingstate (prior to the machining by ECAP).

FIG. 1 shows a schematic illustration of an example of machining of aworkpiece 1 that is pressed through two angled intermerging channels ofa tool 3 by means of a stamp 2, and the refinement of the materialstructure thus achievable.

A particularly notable improvement in the material properties may beachieved by carrying out ECAP multiple times, in particular twice. Thismay also take place in a machining pass when the tool used for ECAP hasat least three channels, of which two in each case merge into oneanother at an angle, as shown by way of example in FIG. 2.

It may preferably be provided that the forming of the workpiece takesplace by hammering in multiple passes, each forming operation having adegree of deformation of 0.05 to 2, preferably 0.1 to 0.5, andparticularly preferably 0.15 to 0.3.

Furthermore, it may be provided that the forming of the workpiece byhammering takes place at a temperature (of the workpiece) of between 10°C. and 600° C., preferably between 12° C. and 380° C., and particularlypreferably between 14° C. and 250° C. Forming of the workpiece byhammering at a temperature of the workpiece of 100° C. and/or 350° C.may also be advantageous.

Hammering, also known as swaging or rotary swaging (for machining ofworkpieces having a circular cross section), is characterized in thattwo or more tools (3) that are situated on the circumferential side ofthe workpiece (1) exert radial forming strokes directed toward aworkpiece center while the workpiece (1) rotates about the workpiececenter relative to the tools (3), as schematically shown in FIG. 3. Arelative movement between the workpiece (1) and the tools (3) along alongitudinal axis of the workpiece (1) allows continuous ordiscontinuous forming machining, even for workpieces (1) whosedimensions along the longitudinal axis are greater than thecorresponding dimensions of the tools (3). The relative movement betweenthe workpiece (1) and the tools (3) along the longitudinal axis (4) ofthe workpiece (1) may preferably be achieved by moving (only) theworkpiece (1) along the longitudinal axis. Alternatively oradditionally, however, a corresponding movement of the tools (3) may beprovided. The strokes performed by the tools (3) may in particular berelatively short (for example, between 0.25 mm and 3 mm, in particularbetween 0.3 and 1.5 mm) and at a relatively high frequency (forexample,1000 per minute and greater). More preferably, it may beprovided that the tools (3) virtually completely enclose the workpiece(1) on the circumferential side, i.e., with only minimal distancesbetween the tools.

According to the invention, hammering may be provided in embodiments inwhich the workpiece (1) undergoes hot forming, warm forming, or coldforming. Various exterior and interior geometries of the workpiece (1)may be shaped by hammering. This may be achieved by using mandrels andby different relative movements of the tools (3) relative to theworkpiece (1).

One advantage of hammering is that only intermittent forming takes placeat a location (tool engagement) with each tool stroke. As a result,fewer overall stresses result in the component than with extrusion, forexample, in which the entire cross section of the workpiece is pressedthrough a bottleneck. Because of this advantage with hammering, thematerial may be subjected to greater deformation without the expectationof crack formation or excessive embrittlement.

One preferred use of a method according to the invention is themanufacture of a resorbable or nonresorbable medical implant, forexample a dental implant or tooth implant. Alternatively, such a medicalimplant may be designed in the form of a screw, a plate, a nail, a wire,a foil, or a scaffold, in particular a stent. The improvement in themechanical material properties, achievable with a method according tothe invention, may have beneficial effects in particular for implants.

Since the primary objective of post-processing of the workpiece byhammering within the scope of a method according to the invention is animprovement in the mechanical material properties, it may be provided touse a method according to the invention for producing a blank or asemi-finished product, i.e., a workpiece that is provided for furtherprocessing.

In particular, the objective of post-processing of the workpiece byhammering within the scope of a method according to the invention may beto achieve a diameter reduction for the workpiece. On account of thelimited length of a workpiece in ECAP due to the stamp stroke of theECPA device used, the length of blanks or workpieces that can beproduced is generally limited, often to less than 500 mm, in particularless than 300 mm. As a result, further machining, for example formanufacturing screws, nails, plates, scaffolds, or stents, onappropriate devices such as lathes, long lathes, laser cutting devices,etc., is usually not cost-effective. In many cases, these devices haveautomatic conveying units, for example automated spindle bores, throughwhich long rods or tubes are to be continuously supplied to themachining process.

Thus, a method according to the invention allows the manufacture ofworkpieces by hammering, for example blanks or semi-finished productssuch as rods, tubes, etc., whose lengths after the hammering may be ≥500mm, preferably ≥1000 mm, and particularly preferably ≥2000 mm, and whichmay thus be further processed in a cost-effective manner.

The workpiece, i.e., the semi-finished product or the blank, may thenundergo further processing, for example machining, to manufacture acomponent having a defined final contour, such as a resorbable ornonresorbable medical implant, for example a dental implant or toothimplant. Alternatively, such a medical implant may be designed in theform of a screw, a plate, a nail, a wire, a foil or a scaffold, inparticular a stent.

On the other hand, in principle hammering also allows shaping of amachined workpiece, characterized by a great freedom of shape and verygood dimensional stability (achievable tolerances of <0.03 mm, forexample). Accordingly, it may also be provided to use a method accordingto the invention for manufacturing a component in such a way thatpredefined final contours of the component are produced by thehammering. Further post-processing may thus be dispensed with, so thatthe manufacturing costs for such a component may be kept low.

In one possible embodiment according to the invention, the hammering iscarried out by means of a so-called double rotation unit (see FIG. 4).This means that the tools and the component, which is guided by rollers,for example, rotate relative to one another either in the same directionor in opposite directions. In this way, the rotation of the workpieceitself is largely avoided, and a very large number of impacts may beachieved.

This procedure may be advantageously provided in particular forlarge-scale production (for example, manufacture of at least 1000identical components), while production of blanks in small-scaleproduction (manufacture of fewer than 1000 identical components) may beadvantageous, since the additional costs incurred for post-processingmachining of the blanks, for example, may be lower than the costs ofmultiple rotary swaging tools with which correspondingly differentshapes for the components may be achieved. However, production of blanksmay also be advantageously provided for large-scale production.

In one preferred embodiment of a method according to the invention, itmay be provided that the metallic material includes titanium (puretitanium (Ti) or a titanium alloy) and/or magnesium (pure magnesium (Mg)or a magnesium alloy), in particular resorbable magnesium. Theimprovement in the mechanical material properties of the material,achievable by the post-processing according to the invention byhammering, has been achieved at least with pure titanium and withtitanium alloys, in particular a preferred titanium alloy which inaddition to titanium also includes (at least or solely) zirconium (Zr),preferably a mass fraction of approximately 10% to approximately 20%, inparticular approximately 12% to approximately 14%, and in particularapproximately 13%.

Titanium and magnesium are also suitable, but in particular titanium,due to its good biocompatibility, is a particularly advantageousmaterial for medical implants that may preferably be manufactured usinga method according to the invention.

In principle, the method according to the invention may advantageouslybe suited for machining workpieces made of metallic materials,particularly preferably using light metals (magnesium (Mg) or aluminum(Al), for example) or the alloys thereof. The method according to theinvention is thus also suited, for example, for producing semi-finishedproducts or blanks from resorbable magnesium or magnesium alloys, fromwhich implants may likewise be manufactured, for example by subsequentturning, laser cutting, or other methods.

It may also preferably be provided that the temperature of the workpieceduring the machining by ECAP is at least 200° C., at least 350° C., atleast 450° C., or at least or approximately 500° C. For a workpiece madeof magnesium or a magnesium alloy, in particular a temperature ofbetween 200° C. and 350° C. may be advantageous. In contrast, for aworkpiece made of pure titanium or a titanium alloy, a temperature of atleast 450° C. and in particular 500° C. may be advantageous. If thetemperature of such a workpiece made of titanium is less than 450° C.and in particular less than 500° C. during the machining by ECAP, thismay result in pronounced crack formation in the workpiece due to themachining by ECAP.

In another preferred embodiment of a method according to the invention,it may be provided that the machining by ECAP includes at least four,six, or eight machining passes. A machining pass is understood to mean apressing of the workpiece through an angled transition between twochannels. In this regard, it may be provided that the workpiece ispressed by a tool having more than two channels, wherein two adjacentchannels in each case form an angled transition, and at least two,preferably all, transitions are oriented differently (see FIG. 2).Additionally or alternatively, it may be provided that between themachining passes the workpiece has been turned (in particular with therotational direction remaining the same) about the longitudinal axis bya defined angle in each case, which may preferably be 90° or 60° or 45°.The statement “has been turned” refers to the orientation of theworkpiece relative to the ECAP tool used, between two machining passes.It is particularly preferably provided that the rotations of theworkpiece between the machining passes result in orientations that as awhole encompass at least or exactly 360°.

Within the scope of a method according to the invention, it may also beprovided that the workpiece is additionally pressure-formed (inparticular extruded) before and/or after the machining by ECAP. Furtherimprovement in the mechanical material properties and/or a reduction indimensions of the workpiece may be achieved in this way. Such additionalpressure forming may be provided in particular before the workpiece ispost-processed by hammering.

It may also preferably be provided that the workpiece is additionallyheat treated. Further improvement and/or a targeted setting of materialproperties of the material may likewise be achieved in this way. Theheat treatment may be provided before or after the machining by ECAP,and before or after the post-processing by hammering, and before orafter optionally provided additional pressure forming. The temperatureselected for the heat treatment may be a function of the selectedmaterial, and for titanium or a titanium alloy, for example, may bebetween 480° C. and 780° C., while for magnesium or a magnesium alloythe temperature may be between 120° C. and 580° C. Since the number andduration of such heat treatment steps may vary, cooling in air or bycontact with some other medium, for example water, oil, or a gas such asargon, is possible.

The indefinite articles “a” and “an,” in particular in the claims and inthe description which provides a general explanation of the claims, areunderstood as such, and not as numerals. Accordingly, specificcomponents are to be understood in such a way that they may be presentat least once, and may be present multiple times.

The improvements regarding certain characteristic values of the materialof a machined workpiece that are achievable by use of a method accordingto the invention are explained below with reference to comparativetests.

An alloy composed of titanium and zirconium in a mass fraction of 13%(Ti-13% Zr) was used as material for the workpieces to be machinedwithin the scope of the comparative tests. In the starting state, theworkpieces, made of solid material, had a circular cross section withdiameters of 10 mm or 16 mm. Two of these workpieces in the startingstate (referred to below as “starting workpieces”) were provided in eachcase as comparative samples.

For the machining of the workpieces by ECAP, an ECAP tool was usedhaving straight-running circular channels with a circular cross section,the channels having a cross-sectional diameter of 12 mm that wasconstant over the longitudinal extension, with the channels merging intoone another at a (forming) angle of 120°. The workpieces were turned by90° in each case between individual machining passes during themachining by ECAP.

Due to the 12-mm cross-sectional diameter of the channels of the ECAPtool, those workpieces having a diameter of 16 mm in the starting statewere turned to provide a diameter of down to 12 mm prior to themachining by ECAP (referred to below as “solid material workpieces”). Incontrast, those workpieces having a diameter of 10 mm in the startingstate were enclosed by a tubular sleeve made of pure titanium and havingan outer diameter of 12 mm (referred to below as “sleeve workpieces”).

Most of the sleeve workpieces were machined by ECAP at a temperature of500° C. in two, four, or six machining passes. After four machiningpasses, cracks formed in the material of individual workpieces, inparticular in the material of the tubular sleeve. When these sleeveworkpieces were subjected to further machining passes, ends of thesleeve workpieces routinely broke off. One sleeve workpiece was machinedby ECAP on a trial basis in four machining passes at a temperature of450° C. However, even more pronounced crack formation occurred as aresult.

A first series of eight solid material workpieces was machined by ECAPin four machining passes at a temperature of 500° C. After the machiningby ECAP, these solid material workpieces had much better surface qualitythan the correspondingly machined sleeve workpieces. Seven of thesesolid material workpieces machined by ECAP were provided forpost-processing by either hammering or rolling, while one of the solidmaterial workpieces was provided as a comparative sample.

Also for one of the solid material workpieces, an attempt was made toreduce the forming temperature to 450° C. Four machining passes werecarried out with this solid material workpiece. Here as well, however,severe crack formation and breaking off of the ends occurred.

For this reason, solid material workpieces of a second series werelikewise machined by ECAP at a forming temperature of 500° C., but inthis case with more machining passes than in the first series. It wasshown that more than six machining passes would not be productive, sinceeven with six machining passes, small pieces sometimes break off at theends of the solid material workpieces, and there is only minorimprovement in the mechanical properties. For a solid material workpiecein this second series, the machining by ECAP had to be terminated afterfive machining passes due to extreme crack formation.

Lastly, five solid material workpieces in the second series weremachined by ECAP and provided for further use. Four of them wereprovided for post-processing, either by hammering or by rolling, whileone solid material workpiece was once again used as a comparativesample.

In the post-processing by hammering, the diameter was reduced inmultiple steps at room temperature (approximately 21° C.):

Starting diameter Final diameter (based on (based on Forming theparticular the particular Degree of step forming step) forming step)deformation (ϑ) 1 10.5 9.5 0.2 2 9.5 8.5 0.22 3 8.5 7.5 0.25 4 7.5 6.50.28 5 6.5 6.0 0.16

In the post-processing by rolling, at room temperature (approximately21° C.) in a first forming step the diameter was reduced from 12 mm to 8mm (ϑ=0.81), and in a second forming step was reduced from 8 mm to 6 mm(ϑ=0.58).

The post-processed workpieces and the workpieces provided as comparativesamples were subsequently subjected to either one or more hardness testsor a tensile test.

The Vickers hardness (HV) was determined in the hardness test. For thispurpose, the workpieces that were provided for the hardness test andembedded and polished for this purpose were each measured with ahardness tester (DuraScan 80 from EMCO-TEST Prüfmaschinen GmbH) with aforce of 10 kp (=HV10) according to EN ISO 6507-1. For each workpiece,an average was determined from at least five individual tests(indentations).

The workpieces provided for the tensile tests, which were machinedsolely by ECAP, were reduced to a diameter of 6 mm by turning, the sameas for the starting workpieces. For these workpieces, in addition aparallel measuring length of 30 mm (B6×30 specimens according to DIN50125) was provided. The workpieces provided for the tensile tests,which were additionally rolled or hammered after the machining by ECAP,already had a reduction to a diameter of only 4 mm due to thispost-processing. A parallel measuring length of 20 mm (B4×20 specimens)was provided for these workpieces. The initial strain rate was 3×10⁻⁴s⁻¹for all tensile tests.

The results of the hardness tests are summarized in the following table:

ECAP machining ECAP Post- Standard Type of workpiece passes temperatureprocessing HV10 deviation Starting workpiece (10 mm) — — — 252 3.6Sleeve workpiece 2 500° C. — 290 2.2 Sleeve workpiece 4 500° C. — 3001.3 Sleeve workpiece 6 500° C. — 304 1.3 Sleeve workpiece 4 450° C. —309 8.0 Starting workpiece (16 mm) — — — 239 1.5 Solid materialworkpiece 4 500° C. — 319 1.3 Solid material workpiece 6 500° C. — 3281.6 Solid material workpiece 4 500° C. Rolling 302 9.3 Solid materialworkpiece 4 500° C. Hammering 338 10.7

These results show that the hardness of the material increases as thenumber of ECAP machining passes increases, with the increase beinggreatest for the first machining passes. For the solid materialworkpieces, the increase in hardness is more pronounced than for thesleeve workpieces (+33% after four machining passes, compared to +38%after six machining passes).

The following conclusions may be drawn for the workpieces that wereadditionally rolled or hammered after the machining by ECAP: In thepresent case, rolling reduces the hardness, while hammering results in afurther increase in the hardness. In both cases, however, the hardnessdistribution is not homogeneous. The workpieces that were additionallyrolled are softer in the middle of the cross section, while theworkpieces that were additionally hammered are harder in the middle thanat the edge (see the table below). Such inhomogeneity was not observedin the workpieces machined solely by ECAP.

ECAP machining ECAP Post- HV10: HV10: Type of workpiece passestemperature processing middle edge Solid material workpiece 4 500° C.Rolling 290 ± 3 305 ± 8 Solid material workpiece 4 500° C. Hammering 355± 4 334 ± 7

To make the hardness distribution apparent, for selected workpieces alocation-dependent measurement was additionally carried out with a lowerload (HV1). These measurements show slight inhomogeneity for a startingworkpiece (16 mm) with slightly increased hardness at the edge, alargely homogeneous hardness distribution of a workpiece machined solelyby ECAP (4×ECAP at 500° C.), and in comparison a reduction in hardnessin the center of a workpiece post-processed by rolling, and once againan increase in hardness in the center of a workpiece post-processed byhammering in comparison to the workpiece machined solely by ECAP.

The results of the tensile tests are summarized in the following table.The elongation characteristic values are plastic elongations (i.e.,without the elastic elongation), and all stresses are engineeringstresses (technical stresses).

ECAP Yield Tensile Uniform Elongation machining ECAP Post- strengthstrength elongation at break Necking Type passes temperature processing[MPa] [MPa] [%] [%] [%] Starting — — — 611 782 7.5 25.5 52 workpiece (10mm) Sleeve 4 500° C. — 950 985 1.8 11.8 56 workpiece Starting — — — 603708 13 29 49 workpiece (16 mm) Solid 4 500° C. — 1030 1048 0.5 11.5 64material workpiece Solid 6 500° C. — 1081 1121 1 11 63 materialworkpiece Solid 4 500° C. Rolling 874 887 0.3 0.4 2 material workpieceSolid 4 500° C. Hammering 1347 1361 0.5 5 35 material workpiece

A comparison of these results shows that trends that are recognizablefor the hardness tests also apply to the results of the tensile tests.The material of the workpieces becomes markedly stronger from machiningby ECAP (for example, +48% in the tensile strength after four machiningpasses). Hammering further increases the strength (+30% tensile strengthcompared to machining solely by ECAP), while rolling decreases thestrength. However, the stronger the material of the workpieces, thelower the respective ductility. The elongation at break of workpiecesmachined solely by ECAP is greater than 10%, while it decreases toapproximately 5% due to subsequent hammering. Subsequent rolling resultsin severe embrittlement.

In summary, the following conclusions may be drawn: The strength andhardness of the starting material (Ti-13% Zr) was increased considerablyby machining by ECAP, while maintaining ductility greater than 10%. Uponfurther machining of the workpieces previously machined by ECAP, it wasshown that rolling did not provide good results, since both the strengthand the ductility were greatly reduced. The decrease in ductility wasexpected, since this is a known effect with cold forming, in particularwith rolling, and is referred to as strain hardening or coldembrittlement. The reduction in strength due to the rolling wasunexpected, and is likely due to excessive stress caused by localincreases in strain during deformation of the material, resulting ininternal disruption and microcrack formation, for example. In contrast,hammering further increased the strength (yield strength and tensilestrength greater than 1300 MPa), and resulted in only a tolerablereduction in the ductility.

One application example of a method according to the invention is theproduction of a semi-finished product, which is subsequently provided ona long lathe for manufacturing dental implants. For this purpose, aworkpiece made of Ti13Zr was machined at 500° C. in four machiningpasses by ECAP and subsequently machined by hammering, wherein thehammering resulted in a reduction in the diameter of the cylindricalworkpiece from 20 mm to 5 mm. The length of the workpiece increased from150 mm to 2400 mm. The machining according to the invention resulted inan improvement of the tensile strength, from 750 MPa originally to 1300MPa, and a change in the elongation at break from 25% (as cast androlled) to 5%.

A further application example of a method according to the invention isthe production of a semi-finished product, which is subsequentlyprovided on a long lathe for manufacturing resorbable pins made ofmagnesium. For this purpose, a workpiece made of ZX00 (magnesium +<1%zinc +<1% calcium) was machined at 250° C. in four machining passes byECAP and subsequently machined by hammering, wherein the hammeringresulted in a reduction in the diameter of the cylindrical workpiecefrom 20 mm to 4 mm. The length of the workpiece increased from 150 mm to3750 mm. The machining according to the invention resulted in animprovement of the tensile strength, from 220 MPa originally to 400 MPa,and a change in the elongation at break from 17% (as cast and rolled) to8%.

1. A method for machining a workpiece made of a metallic material, inwhich the workpiece is machined by ECAP, characterized in that after themachining by ECAP, the workpiece is post-processed by hammering, thusachieving a diameter reduction.
 2. The method according to claim 1,characterized in that the forming of the workpiece by hammering takesplace in multiple steps, each forming operation having a degree ofdeformation of 0.05 to 2, preferably 0.1 to 0.5, and particularlypreferably 0.15 to 0.3.
 3. The method according to claim 1,characterized in that the forming of the workpiece by hammering takesplace at a temperature of 10° C. to 600° C., preferably 12° C. to 380°C., particularly preferably 14° C. to 250° C.
 4. The method according toclaim 1, characterized in that the metallic material includes titaniumand/or magnesium.
 5. The method according to claim 1, characterized inthat the metallic material includes zirconium, in a mass fraction ofapproximately 10% to approximately 20%.
 6. The method according to claim1, characterized in that the temperature of the workpiece during themachining by ECAP is at least 200° C., at least 350° C., at least 450°C., or at least 500° C.
 7. The method according to claim 1,characterized in that the machining by ECAP includes at least fourmachining passes.
 8. The method according to claim 1, characterized inthat the workpiece is additionally pressure-formed before or after orboth before and after the machining by ECAP.
 9. The method according toclaim 1, characterized in that the workpiece is additionallyheat-treated.
 10. The method according to claim 1, characterized by themanufacture of a workpiece having a length ≥500 mm or ≥1000 mm or ≥2000mm.
 11. The method according to claim 1, wherein the workpiece is ablank.
 12. The method according to claim 1, wherein the workpiece is amedical implant.
 13. The method according to claim 12, wherein themedical implant is a dental implant.
 14. The method according to claim12 wherein the medical implant is in the form of a screw, a plate, anail, a wire, a pin, a foil, a scaffold, or a stent.